1. Field of the Invention
The present invention relates to a pyran derivative, and more particularly such a pyran derivative that exhibits long wavelength light. Further, the present invention relates to a method for forming the pyran derivative, and a light-emitting element containing the pyran derivative.
2. Related Art
A light-emitting device utilizing light emission from an electroluminescent element (light-emitting element) has been attracted attention as a device for lighting or displaying an image.
In recent years, in the development area for a light-emitting device, the research and development of a light-emitting device capable of displaying a high quality full color image has been accelerated to secure a market of display devices for various information-processing devices such as a TV set or a car navigation system
In order to obtain full color image from a light-emitting device, a plurality of regions, each of which exhibits at least three primary colors, is independently provided to let each the region emit light at the right time.
Various methods have been developed to provide the foregoing regions. One method for providing the foregoing regions is that a plurality of layers, each of which is formed by light-emitting compounds producing different colors, is formed at different sites, and a plurality of light-emitting elements including each the layer is independently provided.
In case of using the foregoing method, light-emitting compounds are required to be selected for the respective emission color. Therefore, light-emitting compounds that exhibit light emission at various wavelengths have been developed.
For example, as a material exhibiting reddish emission, a pyran derivative as disclosed in U.S. Pat. No. 2,814,435 (p.7) is developed. Besides, bis-4H-pyran derivatives, or the like are also developed as disclosed in Unexamined Patent Application No. 2001-19946. Generally, it is known that long wavelength light can be obtained by introducing a sterically bulky alkyl group to a molecular structure of light-emitting compounds. The pyran derivatives disclosed in U.S. Pat. No. 2,814,435 and Unexamined Patent Application No. 2001-19946 exhibit long wavelength light by being introduced with a sterically bulky alkyl group to a molecular structure.
However, light-emitting compounds exhibiting long wavelength light (mainly light-emitting compounds exhibiting reddish emission) have low carrier transportation properties, and so driving voltage of a light-emitting element containing the light-emitting compounds tends to be increased. (For example, see Yoshiharu SATO, “The Japan Society of Applied Physics/Organic Molecular Electronics and Bioelectronics”, vol. 11, No. 1 (2000), 86-99.) Further, the light-emitting compounds may be difficult to be deposited by vacuum vapor deposition.